Sensors can count people in a given area based on the signals that are emitted by the respective people's mobile devices, such as cell phones. People-counting systems as associated with wireless transmissions by personal mobile devices carried on persons have an interest in operating unobtrusively. Thus, to be effective, the system should ideally operate without requiring the user of the mobile device to take any action beyond being within the sensor range. This ideal is frustrated by continuous development of mobile device security and privacy standards.